Stereo trainer



Filed Sept. 2, 1945 2 Sheets-Sheet 1 m j 11 E35 N "1 "5'5 Q \l a g i )--e== Nov. 13, 1945. M. MacNEILLE ET AL 2,388,858

STEREO TRAINER L3 3 cs H a;

' STEPHEN MMACNEILLE 3 GEORGE J. KOCH Us INVENTORS E BY v 41? & AG'T Nov. 13, 1945. I s. M. M NElLLE ET AL 2,388,858,

STEREO TRAINER Filed Sept. 2; 1943 2 Sheets-Sheet 2 STEPHEN M. MACNEILLE GEORGE J. KOCH INVENTORS WWI/M 14M ATT'Y & AG?

Patented Nov. 13,:

Stephen M. MacNellle, Oak Ridge, Tenn, and

George J. Koch, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. 2., a corporation of New Jersey Application September 2, 1943, Serial No. 500,943

18 Claims.

This invention relates to optical instruments, particularly to those for testing and training stereo vision. q i

The primary object of the invention is to provide an instrument for producing stereo images of slight. preferably variable separation. The

images are polarized mutually at right angles to.

permit separation by suitable polarizers for stereo viewing. Preferably the range of separation of the images includes zero.

According to the invention these images are produced by the inclusionof birefringent means such as a pair of Wollaston or Rochon prisms or a single birefringent crystal, in series with an objective. A target, such as a transllluminatcd v splits this image into two images polarized at right angles. To vary the separation of these images,

the birefringent prism is moved back and forth along the optic axis of the objeotive. The objective itself may also move, particularly in the embodiments of the invention where variable magnification is also desired or where a constant conjugate objective, such as two positive lenses of equal power separated by twice the focal length of either, is used.

One preferred form of the invention has two Wollaston or Rochon prisms in series with the objective, one ahead of it and the other following it. One of these prisms is movable axially, and they are oriented oppositely so that for one position of the movable Wollaston or Rochon, the two prisms exactly nullify each other giving zero image separation.

In a stereo training or testing instrument, these images are viewed by the right and left eyes of an observer respectively'through polarizing filters oriented mutually at right angles to each other so that only a single image is seen, but in depth. Variation of the separation of the-images thus produces an apparent variation in depth. A standard comparison reticle may be included in the primary ime plane and will appear at the same distance as the image when the separation of the two images isaero, provided, of course, the observer hasproper stereo vision.

One form of test includes mechanical means to copending application Serial No. 500,944, by

Wittel, Koch and Boon, flied concurrently herewith. This copending application describes vari ous forms of such instruments incorporating the present invention.

Instead of a simple standard reticle, a depth reticie in the form oi a pair of vectographlc images superimposed in stereo register may be used. The two vectographic images areoriented with their vibration axis mutually at right angles and orthogonal to the birefringent means so that one eye sees only one of the vectographic images and vice versa. Theterm vectographic is here usedv in the simplest of its exact meanings, to refer to an image whose density varies with the direction of polarization of the illumination incident thereon. Those familiar only with the stereo forms of vectographs often refer to the pair of superimposed images as a single vectograph whereas more precisely it should vectographs. a

The images in the primary image plane are relayed through a suitable. beam splitter to the right and left eyes of an observer; preferably the beam splitter is positioned in a'coilimated beam between two positive lenses or sets of lenses. The first lens picks up the light from the primary image p and collimates it. After this light is split into two beams, it passes respectively through objectives into focus in the image planes or the right and left eye eyepieces respectively.

Polarizing filters are included in these right and left eye The reticle described above may be positioned in the focal planes of the eyepieces, i. e., in the secondary image planes, which has the advantage that vectographlc reticles are not needed for theproduct of depth, but the disadvantage that the relative position of the two reticles in these secondaryimage planes must be accurately controlled.

' In one form of the invention the principal reticle mark is an etched one accurately in the primary image plane and the depth-marks are in the eyepiece image planes and do not have to be so accurate since their main function is merely to give a fixed sense of depth to the observer.

for moving one of the birefringent prisms and 9 manual means for restoring the prism to the zero setting. An observer attempts to maintain the apparent image at the same distance as the standard reticle, and a record of his effort serves as a test of his stereo acuity. Reference is made 55 ,According to a preferred'embodiment of the invention intended to simulate inverted field types of range finders, a reflecting surface such as a front surface mirror is placed immediately in front of the target lying on the optic aids of the system or approximately on this axis in a, plane parallel to the plane of divergence of the birefringent prism. A shield is included to cut oil light from the part of the target behind the mirreferred to as two 7 plane;

Fig. 2 illustrates the operation of the optical system;

ror so that the rest of the target and its virtual image seen in the mirror constitute the efiectlve different for the two directions of polarization of the incident light.

' According to the invention of F. E. Tuttle, described -in copending application, Serial No. 500,906, filed concurrently herewith, this mirror system may be combined with a half-wave retardation plate over /2 of the image in the primary image plane. A half-wave retardation plate effectively rotates the polarization of light through 90 so that a pair of images seen ortho-stereoscopically in /2 of the field correspond to a pair ,seen pseudo-stereoscopically in the other half of the field. The above-mentioned vectodye filter, if placed optically ahead of the half-wave plate in this case, colors the ortho pair of images opfpositely to the pseudo pair.

. Other advantages and preferred embodiments of the invention are described below in connection with the accompanying drawings, in which:

Fig. "1 shows the optical system of a stereo. testing instrument incorporating the invention. Figs.

. 1A and 1B illustrate forms of comparison standard reticles for use in this instrument, Fig. 1C illustrates a half-wave retardation plate to be used in the image plane, and Fig. 1D shows a vectodye filter which may be used in the image Figs. 3 to 5 illustrate various forms of birefringent devices useful in the invention;

Figs. 6 and '7 illustrate optical systems tive to that shown inFig. 2;

Figs. 8 to 12. show the arrangement of alternathe images in the primary image field with various forms of the invention. r In Fig. 1 light from a lamp in through a light diffusing screen Ii illuminates a target l2, for example in the form of a picture of aboat. An

objective I3 forms an image of this target in the primary image plane I4, which includes a field lens 15. This image is relayed by a collimating lens I6 through a beam splitter consisting .of a

semitransparent surface I! and a reflecting surface IE to be brought to focu by lenses l6 in secondary im ge planes at the focus of the eyepleces to be viewed respectively by the right and left eyes of an observer. According to the invention birefringent means, consisting of two Wollaston prisms and 26, is'included in series with the objective l3 to split the image into two images in the principal image plane l4, polarized mutually at right angles. Theprism 26 carried by a T mount 21 is axially movable in guide 26 to provide variable separation of the images. For one position of the prism 26, the effects of the two prisms 25 and 26 exactly nullify each other to give zero image separation This movement of the prism 26 is provided by a lever 29 pivoted at the point 30. This pivot 30 is carried on a m ber en aging a cam 32 driven'by a motor When the images have zero separation, a normal observer with proper stereo vision should see the image apparentlyat the same distance as any standard reticleincluded in this primary image plane l4. Such a reticle is shown as in Fig. 1A.

As described in detail in the Wittel et a1. application, mentioned above, the Wollaston prism 26 is driven back and forth by the cam 32 to vary the apparent image distance while the observer attempts to keep this image distance constant and matched to that of the standard reticle by means of the lever 29. That is, the observer attempts manually to maintain zero separation of the polarized images, and to overcome the effect of the movement of the pivot 38 by the cam 32.

In certain stereoscopic range finders the reticle includes botha mark at a standard or comparison distance and additional marks apparently spaced in depth to aid in adjusting the instrument. To simulate such range finders, a vectographic reticle such as shown in Fig. 1B may be substituted in the image plane M. This vectographic reticle consists of a single mark 46 visible to both eyes and pairs of polarized images 41 difiertances. For versatility the reticle marks 43 are 33 so that the member 3! is moved back and forth against the pressure of a spring 34. Polar izing filter 35 mutually at right angles and included in the right and left eye beams respectively permiteach eye to see only one of the images, with the result that these images have an apparent depth depending on their separation.

mountedso thattheymaybeswimg toone side a shownbybrokenlinea.

Another feature of a preferred embodiment of the invention has a mirror 46 positionable as shownby broken llnesonthe optic axis-immediatelyinfrontofthetarget l2 andparalleltothe plane of divergence of the Wollaston prism 25. The mirror ll carries a shield 6| with which to cut of! the unused half of thetarget. The effective target is then the remaining part of the target I2 and its mirror image as seen at the mirror 46. The image ofthis lnthe primary image plane M consists of two halves, one inverted with respect to the other. If a half-wave retardation plate 42, shown in Fig, 10, is placed over one of these images, it will change ,the polarization of the images in that path of the field. Thus the eyes of the observer will see the image in one-' half of the field ortho-stereoccopically and in the other half of the field pseudo-stereoscopically. which half is which depends on the orientation of the polarizing filters 36.

Alternatively. if a v'ecto filter, which is colorless to light polarized in one azimuth and red to light polarized at right angles thereto,-or preferably two such filters, red and blue respectively to light of the two azimuths, is placed in series with the images, the images will appear difierently colored. When combined with the halfwave plate feature, such a color filter, if after the half-wave plate, will give a red image to one eye and blue to the other eye or, if ahead of the halfwave plate, it will give both a red and a blue image to each eye so that the ortho and pseudo pairs of images are oppositely colored, i. e. one red and 'blue and theother blue and red respectively to the two eyes.

trated in some detail. Light from a target 50 is focused by an objective 6| in an image plane 52. This light is split by a Wollaston prism 53 into two beams represented by rays 54 and 55 respectively. If no further birefringent devices were In Fig. 2, the operation of the invention is illus-' assasss included in the system these two beams 54 and 55 would come to focus forming two images 58 and 51 whose separation would depend on the distance of the prism 53from the target til. However, a second Wollaston prism 88 is included oriented oppositely to the prism 53 so that it bends the beams in opposite directions causing both sets of rays to converge to form a single image 59. If the prism 58 is moved along the optic axis the two images separate, and the separation can vary in either direction from zero.

The operation ofa Wollaston prism is shown approximately in Fig. 3 in which two quartz prisms 6i and 62 are cemented with their optic axes oriented at right angles as indicated by the shading, that is, at right angles to each other and also at right angles to the optic. axis of the system.

In Fig. 4 a Rochon prism is illustrated made up of two quartz wedges 63 and 64 which difier from the arrangement shown in Fig. 3 by having the optic axis of the wedge 63 parallel to the optic axis of the system. In Fig. 5 a single birefringent crystal 65 such as quartz or calcite is shown, the amount of separation of the light rays depending on the tilt of this crystal relative to the optic axis of the system.

An interesting embodiment of the invention is shown in Fig. 6 in which light from a target 10 is focused by a constant conjugate objective made of lenses H and I2 on a primary image plane it. These lenses H and I2 have the same pow r and are separated by the sum of their focal lengths. Between the lenses is a birefringent device consisting of two Wollaston prisms it, preferably of equalpower so asto give separation of the images without change of vergence. The whole unit including the lenses H and i2 and the prisms it carried in a mount is axially movable by means of'a rack 16 and a pinion ill.

A somewhat simpler arrangement for the same purpose is shown in Fig. 7 wherein a single crystal 80 is used in place of the pair of Wollaston prisms. When the lens system is set with the target at the focal plane of one of the lenses, the light between the lenses is collimated, and any shifting of the beams due to the crystal 80 is nullified when the beams are again brought to focus by lens 72. For any otherposition of the system relative tothe image planes l0 and 13, the images in the plane 13 become separated,

approximately in proportion to the distance between this plane and the focal point of a lens 12 On the other hand, if a variable magnification system is used, the change in magnification may be in the same direction as the change in 'appar-,

ent distance (i. e., becoming smaller as it appears at right angles to each other so that one image has one color and the other image has the other color, for example, red and blue.

Having thus described various embodiments of our invention, we wish to pointout that it is not limited to these structures, but is of the scope of the appended claims.

What we claim and desire to secure by Letters Patent of the United States is:

1. An instrument for testing and training stereoscopic vision, comprising a target, an objective.

for forming an image 'of the target in a primary image plane, birefringent means in series with the objective for splitting the image into two images polarized at right angles, means for moving at least part of the birefringent means axially and continuously to vary the image separation, means for binocularly viewing the polarized images. including polarizing filters respectively for the right and left eyes of the observer mutually I prisms on opposite sides of the objective, one fixed to recede) or vice versa, depending on the orien- 1 tation of the. viewing filters.

Fig. 8 shows the field of view when thereticle I4 is in place but neither the half-wave plate 42 nor the mirror 40 is used. Fig. 9 snows the field when the mirror 40 is in place. Fig. 10 shows the field when both the mirror 40 and the halfwave retardation plate 42 are in place. Fig. 11 shows the field when the half-wave retardation plate 42 is in place, but the mirror 40 is not used. Fig. 12 shows full field coincidence without either the mirror 40 or the plate 42, but including a twocolor field provided by a vectodye filter over the whole of the image plane l4.- Such a vectodye filter is shown in Fig. 1D. The filter may-be neutral to light polarized in one azimuth and colcred to light polarized at right angles thereto, or two such filters or diner-ent colors may be used graphic stereo separations in and the other movable and oriented to nullify each other and to give zero separation for one position only of the movable prism.

4. An instrument according to claim 1 in which a depth comparison standard reticle is included in the primary image plane.

- 5. An instrument according to claim 1 in which a comparison standard reticle made of vectostereoscopic register is included in the primary image plane, the vectographic axes being respectively parallel to those of the images.

6. An instrument according to claim lin which the viewing means includes eyepieces and means for relaying the polarized images to form relayed images in secondary image planes at the focus of the eyepieces.

7. An instrument according to claim 1 in which the viewing means includes at least one lens for relaying an image from the primary image plane to a secondary image plane and in which is included a depth comparison standard reticle and standard with means for moving said reticles a1- temativelyin and out of said planes.

9. An instrument according. to claim I'includ- "ing'a reflecting surface lying substantially on the optic axis ofthe objective between the target and the objective parallel to the plane of divergence of the birefringent means and means for preventing light from the part of the target behind the reflecting surface from reaching the objective whereby the'other partof the target and a mirror image thereof form the effective target.

10. An instrument according to claim lincludin: a vectodye filter in the primary image plane to diil'erentlally color the images, the vecto axes of the filter being approximately parallel to those of the images.

11. An instrument for stereoscopic vision comprising a target, an objective for forming an image of the target in a primary image plane, a field lens in the primary image plane, a second objective at its focal length from the primary image plane for collimating light therefrom, a beam splitter in the collimated beam for forming right and left eye beams, a lens in each of the letter beams for focusing the light in secondary image permit stereoscopic viewing or the images.

12. An instrument according to claim 11 in-- cluding means tor moving at least part of the birefringent means continuously along the optic.

axis of the objective to vary the separation of the polarized images.

13. An instrument according to claim 11 ineluding a depth comparison standard reticle in at least one of the image planes.

14. An instrument according to claim 11 including ,a vectodye filter in the primary image plane to diflerentially color the images, the vecto axes of the filter being approximately parallel to those of the images.

15.'An instrument according to calm 1 in which the target is a transilluminated picture.

16. An instrument according to claim 1 in which the birefringent means includes two birefringent parts, one fixed and one movable oriented to nullify each other and give zero sepa: ration of the images for one position of the movable part.

17. An instrument according to claim 1 in which the objective is a constant conjugate one and is also moved along its axis by said moving means.

18. An instrument according to claim 1 in which the objective comprises two equal power positive lenses separated by twice their focal length, the birefringent means is between the two lenses and has lateral separating power without verging power and said moving means moves the objective and the birefringent means as a unit alongsaid optic axis.

STEPHEN M. MQCNEKLE. GEORGE J. KOCH. 

